Maskless vortex phase shift optical direct write lithography

ABSTRACT

The present invention provides methods and apparatus for accomplishing a optical direct write phase shift lithography. A lithography system and method are provided wherein a mirror array is configured to generate vortex phase shift optical patterns that are directed onto a photosensitive layer of a substrate. The lithography methods and systems facilitate pattern transfer using such vortex phase shift exposure patterns.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of U.S. Provisional Patent ApplicationNo. 60/578,890, filed Jun. 10, 2004, entitled: “Vortex Phase Shift MaskApplied to Optical Direct Write” which is incorporated herein byreference in its entirety for all purposes.

This application also is also related to the U.S. Utility patentapplication Ser. No. 10/825,342, filed 14 Apr. 2004, which applicationis incorporated herein by reference in its entirety for all purposes.

This application is also related to the U.S. Utility patent applicationSer. No. 10/993,603, filed on 19 Nov. 2004, entitled: “Process AndApparatus For Generating A Strong Phase Shift Optical Pattern For Use InAn Optical Direct Write Lithography Process” which application isincorporated herein by reference in its entirety for all purposes.

This application is also related to the U.S. Utility patent applicationSer. No. 10/988,087, filed on 12 Nov. 2004, entitled: “Process AndApparatus For Applying Apodization to Maskless Optical Direct WriteLithography Process” which application is incorporated herein byreference in its entirety for all purposes.

FIELD OF THE INVENTION

The present invention relates to methods and apparatus for formingpatterns on semiconductor wafers and other substrates. Moreparticularly, the present invention relates to methods for using vortexphase shift patterns in optical direct write lithography to improve thequality of phase shift patterns formed on substrates and/or wafers, forexample, to create semiconductor devices on the wafers.

BACKGROUND

Designers and semiconductor device manufacturers constantly strive todevelop smaller devices from wafers, recognizing that circuits withsmaller features generally produce greater speeds and increased packingdensity, therefore increased net die per wafer (numbers of usable chipsproduced from a standard semiconductor wafer). To meet theserequirements, semiconductor manufacturers have been forced to build newfabrication lines at the next generation process node (gate length). Asthe critical dimensions for these devices grow smaller, greaterdifficulties will be experienced in patterning these features usingconventional photolithography.

Conventional photolithography methods used for pattern generationinvolve exposing a light sensitive photoresist layer to a light source.The light from the source is modulated using a reticle, typically achrome on quartz mask. The patterns formed on the reticle aretransferred to the photoresist layer using typically visible orultraviolet light. The areas so exposed are then developed (for positivephotoresist) or, alternatively, the shaded areas are developed fornegative type photoresist. The developed regions are then washed awayand the remaining photoresist pattern used to provide an etching maskfor the substrate.

One particularly difficult set of problems in the industry concerns theability to form small “pillars” and/or “holes” in substrate. As is knownto those having ordinary skill in the art, a laundry list ofdifficulties is encountered when smaller and smaller diameter holes andpillars are desired. This is especially the case for, for example, holeshaving diameters of about 200 nm or less. Another process difficultycurrently encountered is the relative inability to form two differentsize holes (pillars) in the same process layer. This results in the needfor altering the design of the substrate or increasing the number ofprocess steps required to achieve the desired surface conformation(reducing throughput).

Thus, what is needed is an improved lithography process capable ofovercoming some of these problems. Thus, the present invention providesimproved fabrication and patterning methods useful in chip fabricationprocesses as well as other microscale substrate fabrication processes.

SUMMARY OF THE INVENTION

To achieve the foregoing, the present invention provides a opticaldirect write lithography system and method capable of generating vortexphase shift optical exposure patterns that are directed onto a substrateto facilitate pattern transfer in an optical lithography process.

A method embodiment of the invention involves providing a substratehaving formed thereon a photosensitive layer. A mirror array comprisinga plurality of movable mirrors is configured in a desired vortex phaseshift optical pattern. The mirror array is illuminated to form aresultant vortex phase shift exposure pattern associated with the vortexphase shift optical pattern of the mirror array. The exposure pattern isdirected onto the photosensitive layer of the substrate where it exposesthe photosensitive layer to facilitate pattern transfer to thephotosensitive layer.

In another embodiment, the invention includes an optical direct writelithography system. The system includes a mirror array comprising aplurality of mirrors arranged in plurality of tiles configured in vortexphase shift optical patterns enabling the generation of a vortex phaseshift exposure patterns. The system includes an illumination source fordirecting light onto the mirror array to produce phase shift exposurepatterns. The system includes optics configured to project the phaseshift exposure patterns onto a substrate and a stage for holding thesubstrate in the exposure pattern to facilitate pattern transfer ontothe substrate.

In another apparatus embodiment, the invention comprises a mirror arrayfor use in a maskless lithography system. The disclosed mirror arrayembodiment includes a plurality of mirrors arranged in a vortex phaseshift optical pattern enabling the generation of a vortex phase shiftexposure pattern when illuminated. Moreover, such an array featuresmovable mirrors that can be reconfigured in accordance with the needs ofa user.

These and other features and advantages of the present invention aredescribed below with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description will be more readily understood inconjunction with the accompanying drawings, in which:

FIG. 1 is a simplified schematic diagram illustrating an optical directwrite lithography system in accordance with the principles of theinvention.

FIGS. 2A-2E are simplified diagrams that illustrate several possiblemirror array configurations capable of producing vortex phase shiftoptical patterns in accord with some embodiments of the invention.

FIG. 3A is a simplified schematic depiction of a portion of a mirrorarray embodiment configured to generate an eight phase vortex phaseshift exposure pattern in accordance with the principles of theinvention.

FIG. 3B is a simplified schematic depiction of an illumination patternproduced by a vortex phase shift exposure pattern in accordance with theprinciples of the invention.

FIG. 3C is a simplified schematic depiction of a portion of anothermirror array embodiment configured to generate an eight phase vortexphase shift exposure pattern in accordance with the principles of theinvention.

FIGS. 4A and 4B are simplified schematic diagrams that illustrateexample tile configuration embodiments capable of producing vortex phaseshift optical patterns in accord with some embodiments of the invention.

FIG. 5 is a flow diagram illustrating operations in performing opticaldirect write vortex phase shift lithography processes to pattern asubstrate in accordance with an embodiment of the present invention.

It is to be understood that in the drawings like reference numeralsdesignate like structural elements. Also, it is understood that thedepictions in the Figures are not necessarily to scale.

DETAILED DESCRIPTION

The present invention has been particularly shown and described withrespect to certain embodiments and specific features thereof. Theembodiments set forth hereinbelow are to be taken as illustrative ratherthan limiting. It should be readily apparent to those of ordinary skillin the art that various changes and modifications in form and detail maybe made without departing from the spirit and scope of the invention.

Implementations of the disclosed invention concern direct write opticallithography systems. Such systems are recently invented, for examplebeing discussed in the previously referenced U.S. Utility patentapplication Ser. No. 10/825,342, filed 14 Apr. 2004. Also,implementations of direct write optical lithography systems are taughtin the concurrently filed U.S. Utility patent application Ser. No.10/993,603, entitled “Process and Apparatus for Generating a StrongPhase Shift Optical Pattern for Use in an Optical Direct WriteLithography Process”, which application is incorporated herein byreference in its entirety for all purposes. In one example, the use ofpiston and tilted mirrors is described in “Optical Analysis ofMirror-Based Pattern Generation” by Y. Shroff, Yijian Chen, and W. G.Oldham; Proceedings of SPIE, Vol. 5037 (2003), the entire disclosure ofwhich is incorporated herein by reference for all purposes. As a furtherexample, integrated circuits comprising microelectronic mirror devicesare available commercially. For example, Texas instruments, Inc. ofDallas, Tex. produces a Digital Micromirror Device (DMD) comprising anarray of microscopically small square mirrors, each mirror correspondingto a pixel in the projected image. The individual micromirrors arevertically displaced (i.e., the mirrors are configured to be raised andlowered while their reflective surfaces remain substantially co-planar).Additionally, such mirrors can be configured so that the mirrors are allsubstantially co planar.

Such systems use programmable optical mirrors in a maskless lithographysystem to form desired phase shift optical patterns on a substrate. Suchmaskless direct-write lithography systems use an array of mirrorsconfigured to operate in phase shift mode to generate a desiredlithography pattern which is projected onto a substrate. The apparatususes the mirror array to reflect light onto a photosensitive layer (forexample, a photoresist layer) of a target substrate (e.g., a wafer orother substrate (for example, a reticle)) to achieve pattern transfer.

In the following detailed description, fabrication methods and apparatusfor implementing direct write optical lithography systems to generatevortex phase shift exposure patterns is set forth. Such systems employmirror arrays configured to generate vortex phase shift image patterns.These image patterns are projected onto a desired surface to achievepattern transfer to fabricate surface patterns on the affectedsubstrate.

As a general principle, the embodiments of the invention include amirror array configured in a vortex phase shift optical pattern that cangenerate vortex phase shift exposure patterns when illuminated. Thevortex phase shift exposure patterns are projected onto a substrate tobe patterned. Typically, this means a substrate having a photosensitivelayer formed thereon. When the photosensitive layer is exposed to thevortex phase shift exposure pattern it becomes photo-lithographicallypatterned. The patterned layer is then developed and then treated byfurther processes to for surface structures of a desired type on thesubstrate.

In accordance with embodiments of the invention, a lithography systemilluminates a vortex phase shift mirror array to generate a desiredvortex phase shift exposure pattern (or image pattern) which is directedonto a substrate. In such an embodiment a light source is directed ontoa mirror array configured as vortex phase shift optical pattern togenerate a spiraling diffraction pattern that forms a desired set of(constructive and destructive) interference patterns which areselectively de-magnified and projected onto a substrate. In general, theabove described interference patterns generate a pattern of dark andlight regions that can be use to photo define patterns on a substrate.In one embodiment, the vortex phase shift exposure pattern generates apattern of dark spots can be used to define a pattern of openings(holes) or alternatively define a pattern of pillars in a layer ofphotosensitive material. This, as is known to those having ordinaryskill in the art, can be controlled by the nature of the photosensitivematerial used to pattern the substrate. For example, a positive ornegative photoresist can be chosen. Commonly, the substrate (e.g., awafer or other substrate (for example, a reticle)) is covered with alayer of photosensitive material (for example, a photoresist material orother photoimageable material) which is exposed using the image patternproduced. Subsequently, the photosensitive material is developed andselectively washed away to define a desired pattern in thephotosensitive layer. This patterned layer can then be used to transferpatterns onto the substrate.

FIG. 1 is a simplified schematic diagram illustrating one embodiment ofan optical direct write system configured in accordance with anembodiment of the present invention. The system 100 uses an illuminationsource 108 to generate an off-axis light beam 109 that is projected ontoa mirror array 102. In one implementation the source 108 includes anaperture 108 a. Thus, light generated by the source 108 passes throughan aperture 108 a which generates off-axis light beams 109 that aredirected into a beamsplitter 110 and through an optical system 112.After passing through optical system 112, the off-axis light beams 109are directed onto a mirror array 102. The mirror array 102 is configuredto generate controlled phase differences in the light from the off-axislight beams 109. Light reflected by the mirror array 102 is passedthrough the optical system 112 and beamsplitters 110, 114 and directedonto target wafer 104.

The illumination source 108 may be any illumination source capable ofgenerating electromagnetic waves sufficient to reflect from the mirrorarray 102 and to induce chemical changes in a photosensitive layer onthe wafer 104. Preferably the illumination source 108 is an intermittentsource, capable of exposing the wafer during selected periods of acontinuous scan movement of the light beam relative to the wafer.Commonly (but not exclusively), the illumination source 108 is acoherent light source. In one embodiment the illumination source 108 isan ArF excimer laser producing 193 nm (nanometer) output. Alternativesources, include but are not limited to, 157 nm and 248 nm sources aswell as narrowly filtered light beams (such as an I-line light beam) canbe used. The optical system 112 is typically a demagnifying projectionoptical system of a type known to those having ordinary skill in theart. However, many types of optical systems can be implemented.Moreover, the inventors contemplate systems without such optics.

The off axis light 109 from the source 108 is directed onto a mirrorarray 102 and projected onto the target substrate (here target wafer104) using, for example, beamsplitters 110, 114 and projection opticalsystem 112. As is known to those of ordinary skill many otherarrangements are possible and can facilitate projecting a desired lightpattern onto the substrate in accordance with the principles of theinvention. In particular, in one alternative configuration theprojection optical system 112 can be arranged between a beamsplittingoptic 114 and the wafer 104. Additionally, it is especially pointed outthat arrangements having fewer or no beamsplitters can be used.

In general, the system 100 uses a programmable mirror array 102 tomodulate the light flux from the illumination source 108. Generally,this means configuring the mirror array 102 to generate a vortex phaseshift exposure pattern (to be discussed in greater detail below) that isprojected onto a substrate 104. The illumination source 108 generates anoptical beam 109 that is passed through a projection optical system(e.g., optics 110, 114, 112) onto the substrate 104. In particular, thebeam 109 is directed onto a programmable mirror array 102 configured invortex phase shift optical pattern for generating a vortex phase shiftexposure pattern in the light reflected by the mirror array 102. Thislight can be de-magnified by focusing and demagnification optics 112.After passing through the focusing and demagnification optics 112 thevortex phase shift exposure pattern is directed (e.g., usingbeamsplitter 110 and reflector 114) onto the target substrate 104 whichis mounted on a movable stage 106.

The mirror array 102 can be configured to generate a light diffractionpattern that includes light of differing phase and differingintensities. This is facilitated through the implementation of aplurality of movable mirrors that form part of the array 102 and aregenerally controlled using a control element 115. The mirror array 102can be reconfigured to generate many different patterns in accordancewith the needs of the user. For example, each of the mirrors can beprogrammably actuated using, for example, a mirror array control element115. Such a control element 115 can use software to actuate theindividual mirrors of the array 102 to produce a desired optical patternwhich is then projected onto a target substrate (here wafer 104) toproduce a desired image. As alluded to above, the light from theillumination source 108 may be directed along an optical path 109 andonto the photosensitive wafer 104 by any suitable means as known tothose of skill in the relevant art. In accordance with one embodiment,the mirror array 102 comprises a plurality of mirrors, each of theplurality of mirrors having a very small size. For example, mirrorshaving sides on the order of about 81 (micron) can be used. Theinventors specifically point out that other sizes of mirrors can beused. The light from these mirrors can be demagnified using the focusingand demagnification optics 112 to generate image patterns having a finalpixel size of about 30 nm on a side at the image plane (e.g., on thephotosensitive layer of the wafer 104). Such demagnification can beaccomplished using lens elements of the demagnification optics. Aspreviously indicated, these elements can schematically represent muchmore complicated lens structures. Although the apparatus illustrated isa catiotropic configuration, the scope of the invention is not solimited. That is, any configuration which allows the use of mirrorarrays to direct light to a substrate is expected to be suitable andthus within the scope of the invention. The array 102 typicallycomprises an array of small movable mirrors that can be raised andlowered (vertically displaced) or tilted (or both) to generate areflected optical signal such that at the interfaces between mirrorgroups a phase difference in the reflected light can be introduced.Thus, magnitude of the physical displacement of the piston mirrors isassociated with the phase of the reflected light. In one suitableimplementation, the mirrors of the mirror array are formed as squarereflective surface having dimensions of about 8 μm (micron) by 8 μm. Theoptics can effectively demagnify the dimensions of the mirrors down toany desired size. For example, in one embodiment, the mirrors aredemagnified to a square of about 30 nm on a side. As is known to thoseof ordinary skill many configurations and arrangements can facilitateprojecting a desired light pattern onto a substrate in accordance withthe principles of the invention.

FIGS. 2A-2E depict a number of simplified schematic depictions of somesuitable mirror array configurations capable of generating vortex phaseshift optical patterns in accordance with the principles of theinvention. In general, the mirrors of the array are arranged so that toprovide a series of phase steps according to the needs of the user. Forexample, the number of degrees phase shift in a phase step is determinedusing the following relationship: “phase step”=360°/step increments.Thus, four (4) step increments can be used to produce four 90 degreephase steps. This concept will be illustrated in more detail in thefollowing paragraphs.

For example, with respect to FIG. 2A, an embodiment of a three phasemirror array configuration 200 is depicted. In accordance with theequation above, the three phase mirror array configuration 200 comprisesthree increments such that the phase steps are 120 degrees(120°=360°/3). Accordingly, the mirror array 200 includes a plurality ofmirrors arranged in mirror sets 201, 202, 203. Using an example wherethe mirrors are piston mirrors, the mirrors are displaced to effectphase differences. Accordingly, each mirror set includes a multiplicityof similarly displaced mirrors. For example, in the depicted embodimenta first mirror set 201 can be treated as having zero displacement. Thesecond mirror set can be displaced downward relative to, for example,the first mirror set 201. This downward displacement is such that areflected optical signal from second mirror set 202 is about 120 degreesout of phase (i.e., −120 degrees out of phase) from a reflected opticalsignal reflected from the first mirror set 201. Additionally, the thirdmirror set 203 is further displaced so that the reflected optical signalfrom third mirror set 203 is about 120 degrees out of phase from areflected optical signal reflected from the second mirror set 202 andalso about 240 degrees out of phase from a reflected optical signalreflected from the first mirror set 201. Thus, in this depiction, thefirst mirror set 201 can also be to referred to as having zero phase.Also, the second mirror set 202 can be to referred to as having 120degrees phase (e.g., relative to the first set of mirrors 201). In thesame vein, the third mirror set 203 can be to referred to as having 240degrees phase (e.g., relative to the first set of mirrors 201). Similarpatterns are illustrated for FIGS. 2B-2E. Although described withrespect to a piston mirror implementation, other embodiments using, forexample, tilting mirrors or a combination of tilting and piston mirrorscan be employed.

FIG. 2B depicts an embodiment of a four phase mirror array configuration210. The mirror array 210 includes a plurality of mirrors arranged inmirror sets 211, 212, 213, 214. Again, each mirror set including amultiplicity of similarly displaced mirrors. For example, in thedepicted embodiment a first mirror set 201 can be treated as having zerodisplacement. The second mirror 212 set can be displaced relative to,for example, the first mirror set 211. This displacement is such that areflected optical signal from second mirror set 212 is about 90 degreesout of phase from a reflected optical signal reflected from the firstmirror set 211. Additionally, the third mirror set 213 is furtherdisplaced so that the reflected optical signal from third mirror set 213is about 90 degrees out of phase from a reflected optical signalreflected from the second mirror set 212 and also about 180 degrees outof phase from a reflected optical signal reflected from the first mirrorset 211. Additionally, the fourth mirror set 214 is further displaced sothat the reflected optical signal from fourth mirror set 214 is about 90degrees out of phase from the third mirror set 213 and also about 180degrees out of phase from the second mirror set 212. And additionally,the fourth mirror set 214 is displaced so that it is about 270 degrees(or positive 90 degrees) out of phase from the first mirror set 211.

FIG. 2C depicts a similar embodiment of a six phase mirror arrayconfiguration 220. The mirror array 220 includes a plurality of mirrorsarranged in mirror sets 221, 222, 223, 224, 225, 226. Again, each mirrorset including a multiplicity of similarly displaced mirrors. As before,the first mirror set 211 can operate as the baseline having “zerophase”. The second mirror set 222 can be displaced relative to the firstmirror set 221 about 60 degrees. This displacement is such that areflected optical signal from second mirror set 222 is about 60 degreesout of phase from a reflected optical signal reflected from the firstmirror set 221. Additionally, the third, fourth, fifth, and sixth mirrorsets (223, 224, 225, 226 respectively) are progressively displaced afurther sixty degrees each. So, for example, the reflected opticalsignal from fifth mirror set 225 is about 180 degrees out of phase froma reflected optical signal reflected from the second mirror set 222 andalso about 240 degrees out of phase (or 120 degrees out in the oppositedirection) from a reflected optical signal reflected from the firstmirror set 221.

FIG. 2D depicts a similar embodiment of an eight phase mirror arrayconfiguration 230. The mirror array 230 includes a plurality of mirrorsarranged in mirror sets a, b, c, d, e, f, g and h. Again, each mirrorset including a multiplicity of similarly displaced mirrors. As before,the first mirror set a can operate as the baseline having “zero phase”.The second mirror set b can be displaced relative to the first mirrorset a about 45 degrees. As before, this displacement is such that areflected optical signal from second mirror set b is about 45 degreesout of phase from a reflected optical signal reflected from the firstmirror set a. Additionally, the third through eighth (c, d, e, f, g andh respectively) are progressively displaced a further forty-five degreeseach. So, for example, the reflected optical signal from fifth mirrorset e is about 135 degrees out of phase from a reflected optical signalreflected from the second mirror set b and also about 180 degrees out ofphase from a reflected optical signal reflected from the first mirrorset al.

FIG. 2E depicts a similar embodiment of a twelve phase mirror arrayconfiguration 240. The mirror array 240 includes a plurality of mirrorsarranged in mirror sets in much the same manner as with the forgoingexamples. Again, each mirror set includes a multiplicity of similarlydisplaced mirrors. As before, the first mirror set 241 can operate asthe baseline having “zero phase”. The second mirror set 242 can bedisplaced relative to the first mirror set 241 about 30 degrees(negative 30 degrees). As before, this displacement is such that areflected optical signal from second mirror set 242 is about 30 degreesout of phase from a reflected optical signal reflected from the firstmirror set 241. Additionally, the other mirror sets are eachprogressively displaced a further 30 degrees each. So, for example, thereflected optical signal from fifth mirror set 245 is about 90 degreesout of phase from a reflected optical signal reflected from the secondmirror set 242 and also about 120 degrees out of phase (oralternatively, positive 240 degrees out of phase) from a reflectedoptical signal reflected from the first mirror set 241.

In some embodiments the area of each mirror set is configured to be sameas the area of the other mirror sets. In other embodiments, the areaneed not be the same.

FIGS. 3A-3B illustrate various embodiments and implementations of mirrorarray arrangements. Each mirror array includes a plurality of movablemirrors. These mirrors can be configured as piston mirrors, tiltmirrors, or a combination of tilt and piston operation. Additionally,tilt mirrors can be of two different types. A mirror tilting about anedge (so it tilts like a door) is in a “cantilevered” mode of operation.A mirror tilting about a center axis is in a “torsional” mode ofoperation. Also, such tilt mirrors can be enhanced by including aquarter waveplate that is optically transmissive at the exposurewavelength over a portion of the mirror surface.

The following discussion uses a simplified example comprising asimplified piston mirror implementation. However, the reader is remindedthat the embodiments discussed above can also be employed. Incontinuation, such piston mirrors can be positionally displaced whilemaintaining the reflective face of the mirror substantially parallelwith the plane of the mirror array. In FIG. 3A a portion of aneight-phase mirror array 300 is depicted. This array 300 is configuredas a plurality (four) of eight-phase tiles (four tiles 301, 302, 303,and 304 are depicted here) arranged adjacent to each other. The mirrorsare arranged in mirror sets (e.g., a, b, c, d, e, f & g) that can begrouped together in tiles. FIG. 3A depicts a portion of an arrayillustrating four tiles which are depicted by the darkly outlinedregions 301, 302, 303, 304. Each tile includes a plurality of mirrorsets (i.e., a, b, c, d, e, f & g). Each mirror set comprises amultiplicity of mirrors being displaced to the same degree as the othermirrors in the set. The mirror sets are vertically displaced relative toother adjacent mirror sets. For example, mirror set d is verticallydisplaced relative to adjacent mirror sets c and e. In the eight-phaseconfiguration depicted in FIG. 3A a multiplicity of mirrors areassociated with the mirror set a. In the depicted example, the firstmirror set a has a baseline (zero phase) displacement (e.g., nodisplacement). The second mirror set b has a displacement thatcorresponds to a 45 degree phase change in the reflected signal relativeto the zero phase signal. Additionally, for each mirror set in a tile(e.g., 301) an incremental 45 degree phase change is made by displacingeach mirror set a further 45 degrees from the preceding mirror set. Thiscan proceed, for example, clock-wise until the first mirror set a isagain reached. This process is repeated for each tile. Each tile may beconfigured having the same pattern of tile sets. However, different tilepatterns can also be implemented. For example, it should be observedthat each of the depicted tiles (301, 302, 303, and 304) of FIG. 3A havedifferent displacement patterns. Moreover, many additional and differentpatterns can also be used. Generally, the mirror sets are arranged in aspiral configuration arranged about an axis or center point of the tile.

In some embodiments, the spiral mirror configuration of one tile can bemerely rotated and/or reflected (i.e., a mirror image pattern) relativeto another tile. Using FIG. 3A as an example, tile 302 has a reflected(about axis 320) configuration relative to tile 301. Also, tile 304 hasa reflected (about another axis 330) configuration relative to tile 301.Also, 302 and 304 are reflected relative to tile 303. The inventorspoint out that the mirror groups of the adjacent tiles are in phase witheach other in this embodiment. For example, it is noted that group f oftile 302 is adjacent to group f of tile 303. This alignment of phasebetween tiles reduces the amount of interference between tiles.

FIG. 3B is a simplified schematic diagram of a light intensity map ofthe phase shift exposure pattern generated by the phase shift opticalpattern of the mirror array of FIG. 3A. The depicted tile patterns (asshown in FIG. 3A) are associated with regions of extreme darkness. Forexample, FIG. 3B shows one example phase shift exposure patterngenerated by the tiles depicted in FIG. 3A. Each tile is configured togenerate a dark region. For example, an exposure pattern generated bytile 301 is schematically depicted. A darkest region 301′ is shown. Aslightly more light region 311 is around the dark region 301′. A stilllighter region 312 surrounds region 311. A region 315 of still higherrelative light intensity is also shown. Thus, the tiles can beconfigured to generate a pattern of dark spots that can be used topattern a photosensitive layer (e.g., a photoresist) formed on asubstrate (for example a semiconductor wafer or glass plate). Dependingon the nature of the photosensitive material, a pattern of holes orpillars can be formed using the mirror array.

Mirror array arrangements of the type discussed herein allow greaterflexibility in pattern formation. For example, different tileconfigurations can generate different size dark spots and thereby allowthe formation of different size holes/pillars using the same processstep. For example, in one embodiment an eight-phase tile can be used togenerate a smaller dark spot than a four-phase tile. Additionally, suchvortex phase shift patterns increase the process window. In other words,greater image fidelity can be obtained despite variation in focus andexposure dosage. Additionally, image placement errors can be reducedusing vortex phase shift mirror arrangements.

FIG. 3C depicts another example embodiment where the spiral mirrorconfiguration of one tile is rotated relative to other adjacent tiles.For example, none of the depicted tiles are reflected. Instead, tile 312is rotated 180° relative to tile 311. Moreover, tile 314 is rotated 180°relative to tile 311. The same can be said of tile 313 which is rotated180° relative to adjacent tiles 312 and 314. FIG. 3A has the minimumphase interference between regions 301, 302, 303, and 304. It is notedthat in FIG. 3C the phase difference at the tile interface is not alwayszero. This changes the illumination dose required to print features andthereby alters the critical dimensions possible. The inventors note thatother combinations of rotation and reflection are possible such tilepatterns generally have greater phase differences at the tileinterfaces. Accordingly, these configurations change the illuminationdose required to print features and thereby alters the criticaldimensions possible. The inventors contemplate that other embodimentsthat utilize combinations of tile rotation and reflection can be used toarrange the adjacent tiles so that phase differences at the tileinterfaces of about 135° or less are generated. Such phase interferenceis suitable for use with the present invention. However, the inventorscontemplate that embodiments having phase differences at the tileinterfaces of about 120° are preferred for use with the presentinvention.

FIGS. 4A and 4B illustrate two of many possible tile arrangements usedwith a mirror array in accordance with the principles of the invention.FIG. 4A depicts one embodiment of a four-phase tile arrangement. Thedepicted first mirror set 401 is arranged (in this embodiment) having nodisplacement (and thus in this implementation zero phase). The secondmirror set 402 includes a multiplicity of mirrors (i.e., in thisexample, 36 mirrors) that are displaced relative to the first mirrors401. The displacement is such that a 90 degree phase difference isintroduced between the first mirror set 401 and the second mirror set.The mirrors of the third mirror set 403 are displaced 90 degreesrelative to the second mirror set 402 and 180 degrees relative to thefirst mirror set 401. Finally, the fourth mirror set 404 is displaced 90degrees relative to the third mirror set 403, 180 degrees relative tothe second mirror set 402, an 270 degrees relative to the first mirrorset 401. It is noted that the surface area of each of the mirror sets(401, 404, 404, 404) of the tile 400 is the same. For example, eachdepicted mirror set comprises six mirrors by six mirrors with eachmirror demagnified to about 30 nm×30 nm. Thus, the total size of theprojected tile is about 360 nm×360 nm. Although the surface areas forthe depicted mirror sets are equal, this need not be the case.

FIG. 4B depicts an embodiment of a tile 410 where the mirror sets do nothave equal surface area. The depicted tile 410 illustrates oneembodiment of a twelve-phase tile. A first mirror set 411 is arrangedhaving, for example, no displacement (associated with zero phase). Thesecond mirror set 412 includes a multiplicity of mirrors that aredisplaced relative to the first mirror set 411. In this embodiment, thedisplacement introduces a 30 degree phase difference between the lightreflected by the first mirror set 411 and the light reflected by thesecond mirror set 412. The third mirror set 413 is displaced a further30 degrees relative to the second mirror set 412 and 60 degrees relativeto the first mirror set 411. It should be noted that the surface area ofthe third set is considerable less than the area of the second mirrorset 412 (i.e., six mirrors to 15 mirrors). In like manner, the fourthmirror set 414 is displaced a further 30 degrees relative to the thirdmirror set 413. Thus, the fourth mirror set 414 is displaced 60 degreesrelative to the second mirror set 412 and 90 degrees relative to thefirst mirror set 411. This displacement proceeds in a continuallyincreasing manner as each of the other mirror sets (415-422) aredisplaced.

Additionally, the inventors point out that by reducing the number ofmirrors in each mirror set involved with forming the vortex phase shiftpattern, the CD of the resulting hole or pillar can be changed. Forexample, referring to FIG. 4B, reducing sets 411, 412, 414, 415, 417,418, 420, and 421 from 15 vortex phase shifting mirrors to 14 or somesmaller number of mirrors will result in reducing the strength of thevortex phase interference and therefore increasing the printed CD.

FIG. 5 is a flow diagram illustrating operations for performing opticallithography using a vortex phase shift optical direct write process. Inone method embodiment, a method of forming an image pattern on aphotosensitive layer of a substrate is taught. The flow diagram 500includes an operation of providing a substrate (Step 501). Typically thesubstrate shall include a photosensitive layer onto which image patternscan be transferred. Such photosensitive materials comprisephotoimageable materials such as photoresists and other relatedmaterials. A mirror array comprising a plurality of movable mirrors isprovided (Step 503). The mirrors of the array are then configured into amirror arrangement capable of producing a desired vortex phase shiftoptical pattern in the mirror array when the mirrors are illuminated(Step 505). An image pattern is then formed by illuminating the mirrorarray (Step 507) to form a resultant vortex phase shift exposure patternassociated with the desired vortex phase shift optical pattern in themirror array. In general, an optical beam is projected onto a properlyconfigured mirror array to form a desired vortex phase shift exposurepattern. In one implementation, the created image pattern is directedalong an optical path to onto the photosensitive layer of the substrate(Step 509) to expose the photosensitive layer of the substrate with theresultant vortex phase shift exposure pattern to facilitate patterntransfer to the photosensitive layer (Step 511). Many other lithographytechniques known to those having ordinary skill in the art can beimplemented to accomplish pattern transfer in accordance with theprinciples of the invention.

Although the foregoing invention has been described in some detail forpurposes of clarity of understanding, it will be apparent that certainchanges and modifications may be practiced within the scope of theappended claims. Accordingly, the present embodiments are to beconsidered as illustrative and not restrictive, and the invention is notto be limited to the details given herein, but may be modified withinthe scope and equivalents of the appended claims.

1. A mirror array for use in a maskless lithography system, the mirrorarray comprising: a plurality of mirrors arranged in a vortex phaseshift optical pattern enabling the generation of a vortex phase shiftexposure pattern when illuminated.
 2. The mirror array of claim 1wherein the plurality of mirrors are arranged as a plurality of tileswherein each tile comprises a multiplicity of mirror sets arranged in avortex phase shift optical pattern enabling the generation of a vortexphase shift exposure pattern when illuminated.
 3. The mirror array ofclaim 2 wherein the mirror sets of each tile are arranged in a spiralconfiguration wherein the mirrors of each mirror set are verticallydisplaced relative to the mirrors of an adjacent mirror set.
 4. Themirror array of claim 3 wherein the amount of displacement between themirrors of the mirror sets is associated with a phase difference inlight reflected by the mirrors.
 5. The mirror array of claim 4 whereinthe mirror sets are configured in a spiral pattern arranged about acenter point of the tile to form the vortex phase shift optical patternfor each tile.
 6. The mirror array of claim 4 wherein the tile comprisesthree mirror sets arranged in a spiral pattern about an axis such thatthe amount of displacement between the mirrors of a mirror set isassociated with an about 120 degree phase difference in light reflectedby an adjacent mirror set of the tile.
 7. The mirror array of claim 4wherein the tile comprises four mirror sets arranged in a spiral patternabout an axis such that the amount of displacement between the mirrorsof a mirror set is associated with an about 90 degree phase differencein light reflected by an adjacent mirror set of the tile.
 8. The mirrorarray of claim 4 wherein the tile comprises six mirror sets arranged ina spiral pattern about an axis such that the amount of displacementbetween the mirrors of a mirror set is associated with an about 60degree phase difference in light reflected by an adjacent mirror set ofthe tile.
 9. The mirror array of claim 4 wherein the tile compriseseight mirror sets arranged in a spiral pattern about an axis such thatthe amount of displacement between the mirrors of a mirror set isassociated with an about 45 degree phase difference in light reflectedby an adjacent mirror set of the tile.
 10. The mirror array of claim 4wherein the tile comprises twelve mirror sets arranged in a spiralpattern about an axis such that the amount of displacement between themirrors of a mirror set is associated with an about 30 degree phasedifference in light reflected by an adjacent mirror set of the tile. 11.The mirror array of claim 4 wherein the tile comprises n mirror setsarranged in a spiral pattern about an axis such that the amount ofdisplacement between the mirrors of a mirror set is associated with anabout 360/n degree phase difference in light reflected by an adjacentmirror set of the tile.
 12. The mirror array of claim 5 wherein thespiral pattern of the mirror sets formed on each of the tiles, comprisethe same pattern for each of the tiles.
 13. The mirror array of claim 5wherein the spiral pattern of the mirror sets for a portion of the tilesis different than the spiral pattern of the mirror sets for anotherportion of the tiles.
 14. The mirror array of claim 5 wherein thearrangement of mirror sets for a first spiral pattern of mirror sets ofa first tile is different from an arrangement of mirror sets for asecond spiral pattern of mirror sets for a second adjacent tile.
 15. Themirror array of claim 14 wherein the second spiral pattern of mirrorsets for the second tile is rotated relative to the first spiral patternof mirror sets for first tile.
 16. The mirror array of claim 14 whereinthe second spiral pattern of mirror sets for the second tile is a mirrorimage reflection of the first spiral pattern of mirror sets for firsttile.
 17. The mirror array of claim 14 wherein the second spiral patternof mirror sets for the second tile is rotated relative to the firstspiral pattern of mirror sets for first tile and is also reflected aboutan axis relative to the first spiral pattern of mirror sets for firsttile.
 18. The mirror array of claim 1 wherein the plurality of mirrorscomprise a plurality of movable mirrors that can be controllablydisplaced from an original position in order to generate the vortexphase shift optical patterns.
 19. The mirror array of claim 2 whereinthe plurality of mirrors arranged as the plurality of tiles comprisemovable mirrors that can be controllably displaced from an originalposition in order to generate the vortex phase shift optical patternsfor the tiles.
 20. The mirror array of claim 2 wherein the mirror setsof each tile are arranged in a spiral configuration and wherein each ofthe mirrors of a mirror set are tilted at the same angle but are tiltedat a different angle from the mirrors of other adjacent mirror sets ofthe tile such that they generate phase interference at an interfacebetween two adjacent mirror sets of the tile.
 21. The mirror array ofclaim 20 wherein the mirrors of each tile are cantilevered mirrorsarranged to tilt about a mirror edge.
 22. The mirror array of claim 20wherein the mirrors of each tile are tilted about a central axis. 23.The mirror array of claim 20 wherein each of the mirrors of each tileinclude quarter wavelength waveplates that are optically transparent atan exposure wavelength used to illuminate the mirror array.
 24. Themirror array of claim 1 wherein the vortex phase shift optical patterncomprises a spiraling diffraction pattern.
 25. The mirror array of claim1 wherein the vortex phase shift exposure pattern comprises at least onesubstantially circular dark region.
 26. The mirror array of claim 1wherein the vortex phase shift exposure pattern comprises a plurality ofsubstantially concentric and substantially circular regions of differinglight intensity.